Furnace for pyrolyzing ketenizable organic compounds



Patented Feb. 13, 1951 UNITED STATES PATENT OFFICE I FURNACE FOR'PYROLYZING KETENIZABLE ORGANIC COMPOUNDS David 0. Hull and William R. Saunders, Kingsport, Tenn, assignors to Eastman Kodak Com pany, Rochester, N. Y., a corporation of New Jersey Application July 11, 1947, Serial N0. 760,482

4 Claims.

as described in the Hull patents aforesaid but:

constitutes an improvement thereover in a number of respects as will be set forth herein.

In general the pyrolysisof ketenizable materials is accomplished by various steps such as vaporizing the materials, preheating, and/or superheating the vapors and pyrolyzing the superheated vapors. The temperatures involved for the various operations may range between 300 or 400 C. to 1200 C. or higher. Therefore, it is apparent that for certain of the steps special metal tubes and coils are required for satisfactory commercial operation. In the practice of the invention described herein we prefer to use the coils and a number of other parts manufactured in accordance with the description set forth in companion Patents 2,232,705 and 2,393,778 aforementioned.

The addition of catalyst to the ketenizable ma-' terials to be pyrolyzed, the application of re-' duced pressure to the pyrolysis reaction, the condensation or other treatment of the pyrolysis products, and the like, as carried out in the present invention, (excepting that the larger quantities are processed in the present invention) may be Substantially in accordance with existing practices. Hence, extended description of such. features herein is unnecessary.

As is=readily apparent, the operation of suc pyrolysis processes requires the input of considerable amounts of heat. This has been accomplished heretofore by operating conventional burners in combustion chambers and permitting combustion products in their flow through the apparatus to contact the various coilsthe super heater coil, the pyrolysis coil and the like, as bestpossible, the-organic materials in the coil picking up the heat required for cracking or pyrolysis. I

That is, as may be noted from the drawings of Patent 2,232,705 and. 2,393,773, there i a fixed heating chamber equipped with burners. This" heating chamber is in series with a Pyrolysis. chamber and a preheat or superheat chamber. As shown, these chambers are bricked in, and

hence of a more. or less fixed external .size and.v

construction. As may be further noted from the drawing of the patents aforementioned, the coils within these chambers do not completely fill the space. 7 I

In the prior apparatus and processes, while some increase in capacity might be obtained merely by feeding more materials under a higher pressure and rate of fed through the apparatus.

and supplying more fuel to the burner to furnish a greater amount of heat, such increase in capac. ity obtainable was not of great magnitude, be-v cause if too large a quantity of ketenizable organic.

fluid such as acetic acid vapors, were forced through the coils, at some instant, part of the acid would not be pyrolyzed. Unpyrolyzed product or'partially pyrolyzed-product would be ob-,

tained, thereby reducing the efiiciency and yields obtainable in the process. In other words, existing apparatus may be generally regarded as having a more or less fixed capacity which heretofore appeared to be increasable only by general. enlargement of all parts which would, of course,.

necessitate the enlargement of the external enclosures such as the furnace housing around the various coils.

However, in accordance with the present invention we have found that by certain changes internally of the apparatus, which changes may be more or less readily added to existing equipment, substantially increased capacity may be. obtained without overall alteration of furnace.

size or otherwise materially changing the external furnace housing. In other words, we have,

found that increased capacity may be obtained without generally changing the diameter of the various coils or other overall dimensions of theequipment. However, if desired the diameter of.

the coils may be increased somewhat, as well as. changes made in certain other dimensions, such as increasing the length of the coils, for example,. to such an extent only that it is not required to materially change the housing or other external dimensions of the furnace. We have found that by making the improvements of the present in.- vention, not only isthe capacity. of a furnace of a given external size increased, in that it delivers more desired product, but also the quality of the product and the efficiency of the process are in no way impaired.

This invention has for one object to provide 5, Be made in the construction and the recovery of heat from the effluent combustion gases as these combustion gases pass to the stack. Asshown; coil 3 may be lengthened as at [6 for more completely filling chamber 21. Also, within the space encircled by this coil 3 there may be placed a refractory member, such as 2|. This member may be hollow so that the effluent combustion gases may pass therethrough to the stack. In so passing member 2| is heated and is thereby able to give oif heat to the interior peripheryof coil 3. However, as indicated above, the addition of this improved construction in the space between the last chamber of the series and the stack depends to some extent upon existing constructions. In many existing constructions the improved heat recovery arrangement just described may be incorporated as a supplement to or as a replacement for existing heat recovery devices now used for recovering the last amounts of heat from efiiuent gases prior to their discharge from the stack. A vent, opening, or other passageway means is provided at 24 for permitting the combustion prodnets to escape to the stack.

" Partition wall i2 is so arranged as to provide an opening 26 so that combustion products gain access to chamber 2'! and flow therethrough. The opening 26 connects with the superheater chamber 28 down through which, in that embodiment of the invention being described, the combustion products may flow.

The upper portion of chamber 2B is provided with a brickwork passageway 34 and a plurality of concentric passageways 32 and 33 for connecting the superheater chamber with the pyrolysis ing 35. Since the burner feature may be as shown in the above-mentioned Hull patents, the disclosure of further details herein is unnecessary. Likewise, the furnace housing ll may be constructed from metal parts, brick parts or special composite heat-resisting materials such as metalasbestos and the like.

While in the particular embodiment described the encircled members 22 and 23, have been shown as supported from the base of the furnace housing, these members may be suspended from the upper portion of the housing and the various partition walls correspondingly adjusted for Ohtaining the up and down flow of combustion products through the furnace.

As will be described in detail, it is preferred that a part, such as the surface of, or if desired, the entire partition walls, such as partition walls l2, l3, and I 4, as well as the members 22 and 23 in the space encircled by the coils, be constructed in a special manner and of special materials as will be described in detail under Figure 2.

" Referring to Figure 2 which shows the several members 22 and 23 with the encircling coils re moved, these members in the embodiment shown are made up of a plurality of sections 4|, 42, and 43, for example, held together by rods such as '44," which rods are embedded in the base of the furnace housing or otherwise securely positioned. In general, the overall shape of member 22 and 23 preferably will be that which most closely conforms to the space encircled by the coils but spaced from the coils somewhat to permit easy installation as well as to permit of some expan sion or thermal distortion which may occur at the high temperatures prevailing within the apparatus. In general, the members may be cylindrical with suitable notchout openings therein as may be required to permit the coil to cross over and return to the top of the furnace housing. However, other shapes than cylindrical and constructions such as hexagonal may be employed as long as the space encircled by the coil is at least partly filled. These members, as well as partition walls I2 and I3 and likewise the walls facing the exterior of said coils are preferably constructed of materials having the property of radiant heating and heat absorbing. The various refractory carbides, such as silicon carbide, are preferred, although fire brick or equivalent materials that will withstand the temperatures to which the interior of the units are to be sub-. jected may also be employed. Or, for example, as shown, certain members, as member 2| may be constructed of metal, preferably a metal which will give off heat radiantly and withstand the heating, such as alloy cast irons and steels. For example, the various chromium and nickelchromium irons and steels or aluminum may be used.

The various concentric passageways, such as 33, may be of conventional construction and merely function to conduct the combustion prod: ucts, at a slowed down rate and without channel ing, so that there is an even flow which, when ejected into the respective chambers, flows in a manner conforming to the coils and with relatively even distribution. The checker brick at 34 may be of conventional pattern and is provided for retarding the flow'of the gases from chamber 29 which is the chamber, in the embodiment shown, at the highest temperature. The passageways, such as at 26, may be relatively unobstructed.

In the operation of our process the materials to be pyrolyzed, such as acetic acid vapors, are introduced at 2. Any usual catalyst, such as a phosphate, may be present in the vapors. In passing through the various coils 3, 5, and 8 the materials are suitably heated and pyrolyzed so that the product of the pyrolysis leaving at 9 may be condensed to recover the ketene. While the passage of the ketenizable materials through the apparatus and the reaction products obtained are similar to those described in the above-mentioned Hull companion patentswe have found that the capacity (quantity ofthroughput) is greatly in; creased. This increase is readily apparent from the dataset forth in the table below.

In this table a comparison is made with the throughput and yield through a furnace in which the space encircled by the coils contained no members comparableto members 22 and 23 or other construction in accordance with the present invention. However, in the runs below all other conditions were maintained as nearly the same as possible. That is, the same catalyst and other additions, in the same ratios, were used in each instance. It is, of course, apparent that with the same ratio of catalyst, for example, a greater amount thereof is .fed in accordance with the present invention because a greateramount of acetic acid is fed due to the increased capacity obtainable by the present invention. The units of feed were by weight. The yield represents the percentage of the feed converted to the desired product .-in ca single pass athrough the apparatus. The acid number .another measure, of an empirical nature, of theyeificlency. Thi zmeasure .isapplied to certain :efliuents. .lfzthe numberruns high that indicates more acid'fced .isgoing through the apparatus without conversion than in aninstance where this number is;lw.

Fromlthe above table it will be .observed that in general the capacity (increase of feed) was-increased at least 50 without sacrifice of yield. In other words, for the same external size furnace occupying the same amount of 'iioorspace'in'the plant, it was possible to supply a substantially greater amount of feed to this unit and convert it tothe desired product. Consequently, it may be seen that by the application of the present invention to existing equipment or in the construction of new equipment two of the present units would be approximately equivalent to, or better 'than, three units of prior construction. For the same floor space it is therefore possible to obtain greatlyincreased production or a predetermined production may be obtained'by smaller-floorspace. The advantages are further reflected in that, even thoughthere is substantially increased capacity, the-expense of constructing the furnace housing I I is not materially changed. Also no increase in .costs is required for installing additional controls or'ancillary equipment'for the construction of the present invention which gives increased capacity.

In .other words, the same number of burners for combustion purposes will suffice, although in preferred operation, rather than employing-asingle burner delivering a certain amount of heat, it'is preferred to employ a plurality of smaller burners and burners of a type whichdeliver a radiant heating type of combustion product and heating medium, as it appears that this may contribute to even further increased capacity.

While it is not desired to be bound by any theory of operation respecting the presentinvention or the advantages obtained by the present construction, the following theory concerning the operation of the present apparatus and'process mayconstitute an explanation for the improved results obtainable and is set forth primarily as an aid to a better understanding of the present invention.

--As described at the outset, the present processes of converting and pyrolyzing ketenizablemater'i'als may require operation of the pyrolysis zone at temperatures in excess of 700 or800 "C.-and, for example, even at 900 or 1000" 0., depending upon various factors such as the degree of :reduced pressure on the system, the speed with Whichthe ketenizable materials are being passed through the apparatus and the like. In addition, as. referred to above, the reaction involved in converting a ketenizable material, suchias aceticzacid,

"to ketene is endothermic and consequently:re-

quires a high heat input.

It is known that heat may be transmitted in several ways such as, for example, by "convec- 1 :tiomab'y :conduction, and by radiation. It .is also known that, in general, heat transfer increases as-the-temperature increases. However, .Withalfispect'to heat transfer theheat transferred .by radiation under certain conditions may be .substantially greater than in heat transfer by-conduction. In the particular processes .under. description we have found that the best heat transfer can be obtained primarily by radiation.

In prior constructions where the combustion products comprising the heating medium were permitted .to pass in a baflied manner over --and above the coils, pyrolysis was presumably. accomplished by'heattransferred largely vby convection andconduction.

Inthe construction .of the prcsentinvention wherein the particular members 2|, 22, andii, are positioned within the space encircled by the coils, .as well .as by other members capablesof radiant heating, preferably .on the surface or throughout theseveral partition walls, it isipossible .to increase .the heat supplied by radiation, which is particularly efiective by virtue of its striking .asubstantial portion of the entire ;surface of the various coils (both the inner periphery and outer periphery thereof). By the various checker brick and concentric passagewayarrangements, the heating medium is delayed in the pyrolysis chamber sufiiciently long so that all portions thereof, including member -23, acquire heating energy which is released as radiant heat to the pyrolysis. Similar remarks apply toheating in the several other chambers. In addition thereis also obtained heatinput to the reaction by convection and conduction from .the passage of the heating medium from the burner chamber to the .outlet. flue.

Moreover certain products of combustion, namely the heating medium itself, are capable of giving off thermal energy in the form of .radi antheat. Therefore, by controlling thecombustion in the burner chamber further radiant. heat may be obtained in this manner. In general, .we may use oil, gas, or the like fuels. We prefer to operate the combustion so that the coils donot carbon-up extensively. If carbon forms on the coils, it may ignite and burn on the coils with attendant injury.

However, irrespective of the theory of operation, we have found the construction, as fully disclosed herein, permits a substantial increasein capacity in process and apparatus of the class described and production of ketene of quality andrichness at least as high as that obtainedin prior art operation. As indicated, the external size of the apparatus does not have to be materially increased, if at all, nor is greater floor space required for our apparatus.

It will be apparent that certain other changes may be made without departing from the spirit of the-present invention.

We-claim:

1. An apparatus for the pyrolysis of a ketenizableorganic compound to produceketene which comprises a furnace housing made up of topybottom and side walls and containing three inter-- connected chambers which are separated from each other by partition walls extending partially across the interior of the housing, a vertically extending coil in each of said chambers,

each of said coils extending substantially the entire vertical distance between the top and bottom of the housing, said coils being constructed .of a chromium-containing steel,'means'for.con.- necting :said coils in series, vertically extendingssiliconacarbiderefractory core membersposie tioned within a substantial part of the space encircled by said coils, said refractory members being made up of a plurality of sections held together by means securely attached to the furnace housing and means associated with said apparatus for supplying hot combustion gas to one of said chambers, and means of withdrawing said hot gas from another of said chambers after it has passed through all three chambers and in contact with said refractory core members.

2. An apparatus for the pyrolysis of a ketenizable organic compound to produce ketene which comprises a furnace housing, made up of top, bottom and side walls and containing three interconnected chambers which are separated from each other by partition walls extending partially across the interior of the housing, a vertically extending coil in each of said chambers, each of said coils extending substantially the entire vertical distance between the top and bottom of the housing, means for connecting said coils in series, vertically extending refractory core members positioned within a substantial part of the space encircled by said coils, said refractory members being made up of a plurality of sections held together by means securely attached to the furnace housing, and means associated with said apparatus for supplying hot combustion gas to one of said chambers, and means for withdrawing hot gas from another of said chambers after it has passed through all three chambers and in contact with said refractory core members.

3. In an apparatus for the pyrolysis of ketenizable organic compounds to produce ketene, comprising a furnace housing made up of top, bottom and side walls and containing three interconnected chambers which are separated from each other by partition walls extending partially across the interior of the housing, a vertically extending coil in each of said chambers, means for connecting said coils in series, means associated with said apparatus for supplying hot combustion gas to one of said chambers, and means for withdrawing combustion gas from another of the chambers, after the combustion gas has passed through all three chambers, the improvements characterizing the apparatus which comprises the features that said vertically extending coils extend substantially the entire vertical distance between the top and bottom of the housing and contain vertically extending refractory core members positioned within a substantial part of the space encircled by said coils, said refractory core members being made up of a plurality of sections held together by means securely attached to the furnace housing.

4. An apparatus for the pyrolysis of a ketenizable organic compound to produce ketene which comprises a furnace housing made up of top, bottom and side walls and containing three interconnected chambers for preheating, superheating and pyrolysis, partition walls between the chambers which extend partially across the interior of the housing, a vertically extending coil in each of said chambers, said coils extending substantially the entire distance between top and bottom of the housing, means for connecting the coils in series for preheating, superheating and pyrolysis as aforementioned, vertically extending refractory core members positioned within at least two of said coils, said core members occupying a substantial part of the space encircled by the coils which contain core members therein, said refractory core members being made up of a plurality of sections held together by means securely attached to the furnace housing and means associated with said apparatus for supplying hot combustion gas to one of said chambers and means for withdrawing hot gas from another of said chambers after the combustion gas has passed through all chambers and in contact with the refractory core members aforementioned.

' DAVID C. HULL.

WILLIAM R. SAUNDERS.

REFERENCES CITED The following references are of record in the file of this patent: 

2. AN APPARATUS FOR THE PYROLYSIS OF A KETENIZABLE ORGANIC COMPOUND TO PRODUCE KETENE WHICH COMPRISES A FURNACE HOUSING, MADE UP TO TOP, BOTTOM AND SIDE WALLS AND CONTAINING THREE INTERCONNECTED CHAMBERS WHICH ARE SEPARATED FROM EACH OTHER BY PARTITION WALLS EXTENDING PARTIALLY ACROSS THE INTERIOR OF THE HOUSING, A VERTICALLY EXTENDING COIL IN EACH OF SAID CHAMBERS, EACH OF SAID COILS EXTENDING SUBSTANTIALLY THE ENTIRE VERTICAL DISTANCE BETWEEN THE TOP AND BOTTOM OF THE HOUSING, MEANS FOR CONNECTING SAID COILS IN SERIES, VERTICALLY EXTENDING REFRACTORY CORE MEMBERS POSITIONED WITHIN A SUBSTANTIAL PART OF THE SPACE ENCIRCLED BY SAID COILS, SAID REFRACTORY MEMBERS BEING MADE UP OF A PLURALITY OF SECTIONS HELD TOGETHER BY MEANS SECURELY ATTACHED TO THE FURNACE HOUSING, AND MEANS ASSOCIATED WITH SAID APPARATUS FOR SUPPLYING HOT COMBUSTION GAS TO ONE OF SAID CHAMBERS, AND MEANS FOR WITHDRAWING HOT GAS FROM ANOTHER OF SAID CHAMBERS AFTER IT HAS PASSED THROUGH ALL THREE CHAMBERS AND IN CONTACT WITH SAID REFRACTORY CORE MEMBERS. 